The present embodiments relate to a local coil system and a magnetic resonance (MR) system with reduced interference signals.
In a magnetic resonance system for creating a tomograph, a patient is positioned on a couch in a cylindrical measuring space. A strong magnetic field prevails in cylindrical space. On account of the activation of a gradient coil, the magnetic field includes a gradient. The nuclear spin of atoms is adjusted through the magnetic field. A transmitting antenna arrangement, generally a whole body transmitting antenna arrangement (e.g., a birdcage antenna), is disposed within cylindrical space in order to output magnetic resonance high frequency pulses so as to excite the atoms.
During a magnetic resonance examination, local coils are generally used to receive the magnetic resonance response signals during relaxation of the nuclear spin. Different materials exhibit different relaxation behavior, so that conclusions may be drawn as to the interior of the body of the patient on account of the relaxation behavior. These local coils are receiving antenna modules, which comprise at least one or more receiving antenna elements, generally in the form of conductor loops. The received MR response signals are generally preamplified in the local coil and routed out of the central region of the magnetic resonance system by way of cables to a screened receiver of an MR signal processing facility. The received data is then digitalized and further processed. With many examinations, a plurality of such local coils is already arranged on the patient in order to cover whole areas of the body of the patient.
The mode of operation of magnetic resonance systems is known to the person skilled in the art and described for instance in Imaging Systems for Medical Diagnostics, Arnulf Oppelt, Publicis Corporate Publishing, ISBN 3-89578-226-2.
The local coils are frequently arranged in a so-called local coil mat, which is placed above or below the patient body. In addition, specially molded local coil systems, such as head coils, neck coils or others exist. The signals are currently routed from the local coils to an evaluation facility of the magnetic resonance system by cables. The cables are undesirable since cables cannot be easily routed from the patient couch to the evaluation facility, are perceived as bothersome by personnel since the patient couch is moved with the patient and the local coil mat and the cables are consequently loosely routed.
Approaches for the wireless digital transmission of signals between the local coils and the magnetic resonance system are known. Nevertheless, in this case, electronic components are located in the high frequency field of the body coil. For example, analog-to-digital converters, FPGA, processors, modulators are in the field. These components must prevent any emission of signal parts into frequency ranges falling in the Larmor frequency range of the magnetic resonance system. In addition to the interference signals generated directly in the Larmor frequency range, intermodulation products of several interference signals, which do not lie individually in the Lamor frequency range, may have intermodulation products that are in the Lamor frequency range.